The present invention relates generally to semiconductor devices and more particularly to doping III-V nitride light-emitting devices.
Silicon (Si) is the donor of choice for doping n-type III-V nitrides due to its favorable properties. In particular, during metal-organic chemical vapor deposition (MOCVD), Si atoms can be delivered to the growing crystal by flowing silane (SiH4), which is available as a high purity grade gas. In addition, Si incorporates efficiently onto the gallium (Ga) sites in the gallium nitride (GaN) lattice where it acts as a donor. Further, Si in GaN (SiGa) is a shallow donor with an activation energy for ionization of xcx9c20 meV.
However, with Si doping the achievable n-type conductivity of an III-V nitride layer is limited due to the fact that the incorporation of Si leads to the formation of cracks for heteroepitaxially-grown III-V nitride materials (particularly on sapphire substrates). For a given material thickness, the material cracks when the Si doping level exceeds a certain critical concentration. Likewise, for a given doping concentration, the material starts to crack when the material thickness exceeds a certain critical thickness.
Both a high doping concentration and a large material thickness are desirable to reduce the electrical resistivity of a semiconductor material. For example, for an xcx9c3.5 xcexcm thick GaN material, as typically employed in a light-emitting diode (LED) structure, the doping concentration is limited to xcx9c5e18 cmxe2x88x923. As a consequence of the aforegoing, the series resistance of an aluminum indium gallium nitride (AlInGaN) LED is dominated by the resistance of the Si-doped GaN layer. This is the case for growth on non-conductive substrates such as sapphire where the current passes laterally through the Si-doped GaN layer as well as growth on conductive substrates such as silicon carbide (SiC) and hydride vapor phase epitaxy (HVPE) grown GaN where the current passes vertically through the thick Si-doped GaN layer. Higher doping concentrations and/or thicker n-type GaN materials (for growth on non-conductive substrates) would be advantageous for the fabrication of III-V nitride based LEDs with low series resistance.
Further, in addition to Si, germanium (Ge) and tin (Sn) have been studied as potential donor impurities for III-V nitride materials. However, there are reports on Ge doping experiments where it was concluded that doping with Ge is problematic. In the S. Nakamura, T. Mukai, and M. Senoh, Si- and Ge-Doped GaN Materials Grown with GaN Buffer Layers, Jpn. J. Appl. Phys. 31, 2883, 1992, it is reported that the doping efficiency of Ge is about one order of magnitude lower than for Si. Furthermore, they concluded that the maximum carrier concentration for Ge-doped GaN is limited to xcx9c1xc3x971019 cmxe2x88x923 because at this doping level the surface of the Ge-doped GaN materials becomes rough and shows pits. X. Zhang, P. Kung, A. Saxler, D. Walker, T. C. Wang, and M. Razeghi, Growth of AlxGa1-xN:Ge on sapphire and Si substrates, Appl. Phys. Lett. 67, 1745 (1995), concluded the Ge-doped aluminum gallium nitride (AlGaN) materials have low electron mobilities and that Ge doping is not useful for growing low resistivity materials.
For a long time, a solution has been sought to the problem of material cracking which occurs with Si doping levels exceeding certain concentrations at certain critical thicknesses. Further, Si doping is known to cause the III-V nitride materials to embrittle, which further enhances the tendency of the material to crack, and a solution to this problem has long been sought. It has also been shown that there is a large piezoelectric effect due to the lattice mismatch between GaN and its alloys. For example, an indium gallium nitride (InGaN) layer grown between two GaN layers will have a high piezoelectric sheet charge associated with each interface.
The present invention provides a semiconductor device having n-type device layers of III-V nitride having donor dopants such as germanium (Ge), silicon (Si), tin (Sn), and/or oxygen (O) and/or p-type device layers of III-V nitride having acceptor dopants such as magnesium (Mg), beryllium (Be), zinc (Zn), and/or cadmium (Cd), either simultaneously or in a doping superlattice, to engineer strain, improve conductivity, and provide longer wavelength light emission.
The present invention further provides a semiconductor device using Ge either singularly or in combination, as a co-dopant, with Si and Sn as donor dopants either simultaneously or in a doping superlattice to engineer strain. Unlike Si, the Ge doping concentration can range from xcx9c1019 cmxe2x88x923 to xcx9c1020 cmxe2x88x923 at layer thicknesses of 3 xcexcm and higher without causing cracking problems.
The present invention further provides donor impurities which do not cause embrittlement of III-V nitride materials.
The present invention further provides multi-donor impurity doping for III-V nitride materials to control doping and strain engineering separately.
The present invention further provides highly conductive, n-type, Ge-doped, gallium nitride (GaN) materials for utilization in contact layers of III-V nitride devices.
The present invention further provides a light-emitting device with donor impurities which promote growth of high indium nitride (InN) containing indium gallium nitride (InGaN) light emission layers for light emission at long wavelengths (xcexxe2x89xa7500 nm). This allows the InGaN active region to contain a higher InN composition with higher quality and thus a higher efficiency, longer wavelength light emission or the growth of an AlGaN layer on top of GaN without cracking.
The present invention further provides a light-emitting device co-doped using a combination of Si, Ge, Sn, oxygen (O), magnesium (Mg), beryllium (Be), zinc (Zn), or cadmium (Cd) to improve the conductivity of III-V nitride materials which stabilize the structural integrity of heteroepitaxially-grown III-V nitride materials on lattice mismatched substrates.
The present invention further provides a light-emitting device using different donor dopants for conductive and contact layers.
The present invention further provides a light-emitting device where a bottom layer is doped with Ge and a layer on top doped with a different species (e.g. Si, Sn, or a combination of Si, Ge, and Sn). This permits adjustment of the in-plane lattice constant of GaN closer to the in-plane lattice constant of a ternary compound (e.g., InGaN or aluminum gallium nitride (AlGaN)). This allows the InGaN active region to contain a higher InN composition with higher quality and thus a higher efficiency, longer wavelength light emission or the growth of an AlGaN layer on top of GaN without cracking.
The present invention further provides a method of controlling strain and, thus, the effects of piezoelectricity in III-V nitride layers. Strain engineering plays a major role in controlling piezoelectric interface charges.
The above and additional advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description when taken in conjunction with the accompanying drawings.